Eight brain-surgery patients at a New Hampshire hospital may have been exposed to a rare and fatal disease through potentially contaminated equipment, state health officials announced Wednesday.

Five additional patients in other states might also have been exposed to the rare, degenerative disorder, Creutzfeldt-Jakob Disease, which is similar but not related to "mad cow" disease.

Officials stressed that the risk of infection was "extremely low."

Health officials are nearly certain that a patient who died in August after brain surgery in May at Catholic Medical Center in Concord, N.H., had sporadic CJD, which occurs spontaneously with no known cause. Confirmation will come through an autopsy, which is being conducted at the National Prion Disease Pathology Surveillance Center.

The other patients may have been subsequently infected through surgical equipment that was improperly sterilized. The disease-causing prion - an abnormal protein - is not killed by standard hospital sterilization. Some of the surgical instruments were rented, and the equipment has been quarantined.

"The risk to these individuals is considered extremely low, but after extensive expert discussion, we could not conclude that there was no risk, so we are taking the step of notifying the patients and providing them with as much information as we can," saidJosé Montero, the director of public health at the New Hampshire Department of Health and Human Service. "Our sympathies are with all of the patients and their families, as this may be a confusing and difficult situation."

There is no risk to other patients and employees at the Concord hospital or to the public.

About one in a million people worldwide are infected with CJD, with about 200 people diagnosed annually in the United States. The disease is often confused with mad cow (bovine spongiform encephalopathy), a brain-wasting prion disease transmitted from infected cattle.